Light to moderate long-term grazing enhances ecosystem carbon across a broad climatic gradient in northern temperate grasslands

Edward W Bork; Daniel B Hewins; Eric G Lamb; Cameron N Carlyle; Mark P Lyseng; Scott X Chang; Michael J Alexander; Walter D Willms; Majid Iravani

doi:10.1016/j.scitotenv.2023.164978

Light to moderate long-term grazing enhances ecosystem carbon across a broad climatic gradient in northern temperate grasslands

Sci Total Environ. 2023 Oct 10:894:164978. doi: 10.1016/j.scitotenv.2023.164978. Epub 2023 Jun 17.

Authors

Edward W Bork¹, Daniel B Hewins², Eric G Lamb³, Cameron N Carlyle⁴, Mark P Lyseng⁵, Scott X Chang⁶, Michael J Alexander⁷, Walter D Willms⁸, Majid Iravani⁹

Affiliations

¹ Department of Agricultural, Food and Nutritional Science, University of Alberta, 4-10 Agriculture and Forestry Center, Edmonton, Alberta T6G 2P5, Canada. Electronic address: Edward.bork@ualberta.ca.
² Biology Department, Rhode Island College, 600 Mount Pleasant Ave., Providence, RI 02908, USA.
³ Department of Plant Sciences, University of Saskatchewan, 51 Campus Dr., Saskatoon, Saskatchewan S7N 5A8, Canada.
⁴ Department of Agricultural, Food and Nutritional Science, University of Alberta, 4-10 Agriculture and Forestry Center, Edmonton, Alberta T6G 2P5, Canada.
⁵ Alberta Beef Producers, Government Relations and Policy, Lead 165, 6815-8(th) Street NE, Calgary, AB T2E 7H7, Canada.
⁶ Department of Renewable Resources, University of Alberta, 442 Earth Sciences Building, Edmonton, Alberta, Canada, T6G 2E3.
⁷ Alberta Environment and Parks, Government of Alberta, 2(nd) Floor Provincial Building, 200-5 Avenue South, Lethbridge, Alberta T1J4L1, Canada.
⁸ Agriculture and Agri-Food Canada (Retired), 5403 1(st) Avenue South, Lethbridge, Alberta T1J 4B1, Canada.
⁹ Alberta Biodiversity Monitoring Institute, Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.

PMID: 37336416
DOI: 10.1016/j.scitotenv.2023.164978

Abstract

Grasslands are globally abundant and provide many ecosystem services, including carbon (C) storage. While grasslands are widely subject to livestock grazing, the influence of grazing on grassland ecosystem C remains unclear. We studied the effect of long-term livestock grazing on C densities of different ecosystem components in 110 northern temperate grasslands across a broad agroclimatic gradient in Alberta, Canada. These grasslands stored 50 to 180 t ha^-1C in live and dead vegetation, as well as soil C to 30 cm depth, with the majority as soil organic C (SOC). The mulch layer comprised a large amount of C (~18 t ha^-1C) especially within humid grasslands. Although grazing reduced C densities in litter mass, total ecosystem C was 8.5 % greater under grazing (127.8 t ha^-1) compared to those non-grazed (117.8 t ha^-1), primarily due to increases in SOC and roots. Increases in SOC were consistently observed in the 0-15 cm layer across all climatic conditions, with changes in SOC of the 15-30 cm layer inversely related to aridity. A structural equation model revealed that increased SOC under grazing was indirectly attributed to increases in eudicot rather than graminoid biomass. In addition, SOC increased with graminoid quality (i.e., a reduced carbon to nitrogen ratio), which together with elevated eudicots, increased litter and mulch C, and ultimately enhanced SOC densities. When applied to spatial maps of habitat type and land use (livestock grazing) activity across the region, an area of ~3.8 M ha of grassland was projected to contain an additional 17.1 M t of C under grazing, primarily in mesic grasslands, worth an estimated $3.1 B (Cdn.) under current C valuation guidelines in Canada. Overall, these results highlight the importance of grasslands for C storage and establishing policies that maintain and promote their sustainable use, including light to moderate grazing.

Keywords: Aboveground carbon; Cattle grazing; Mulch carbon; Soil organic carbon; Vegetation composition.

MeSH terms

Alberta
Animals
Carbon / analysis
Ecosystem*
Grassland*
Livestock
Soil / chemistry

Substances

Carbon
Soil